In wireless networking, a wireless access point (“wireless AP” or “WAP”) is a device used to generate a wireless local area network (“wireless LAN” or “WLAN”) to allow a number of wireless client devices to communicate using radio transmissions within a small/local geographical area such as that of a home or office. It is common for wireless access points generating WLANs to operate in accordance with the IEEE 802.11 family of wireless protocols, more commonly known as WiFi or Wi-Fi™.
WLANs generally can have a range of tens of meters which is generally large enough to cover a home or small office. Despite the possible range, the exact coverage and data rates obtainable in a given location are dependent on the transmission power, frequency band of the WLAN and signal attenuation caused by the presence of obstructions and interference.
The transmission power is limited by licensing restrictions set by a radio regulator and also power constraints of the wireless devices themselves. The frequency is relevant because IEEE 802.11 operates in the 2.4 GHz and 5 GHz range of unlicensed radio spectrum. The 2.4 GHz frequency range used in IEEE 802.11b/g/n provides longer range than the 5 GHz frequency so suffers less from attenuation caused by obstructions, but WLANs operating in 2.4 GHz are more susceptible to interference from other 2.4 GHz WLANs as well as from other devices operating in the non-licensed spectrum range such as Bluetooth™ devices, cordless landline telephones and microwave ovens.
Within a WLAN band of frequencies, there are generally several channels, each channel covering a smaller range of frequencies. Each channel on the 2.4 GHz spectrum is 20 MHz wide. The entire spectrum is less than 100 MHz wide (in most of world it is only 83.5 MHz wide, including guard bands) and the centers of neighboring channels are separated by 5 MHz. This means that there is some overlap between most of the channels. Due to this and the possibility of interference from WLAN and other devices operating in the same spectrum range, many wireless access points allow for channel selection within a band (and some allow for band selection as well).
In contrast to the 2.4 GHz band, the 5 GHz band used in IEEE 802.11n/ac has a higher peak bandwidth and operates in a less congested range of spectrum with more available channels, but due to the shorter wavelengths, has a shorter range for a given transmission power and is more sensitive to attenuation caused by the presence of walls. In some applications, 5 GHz WiFi is recommended for short-range (i.e. based on the distance between the wireless access point and the user device), high-bandwidth uses such as video data streaming, while 2.4 GHz WiFi is recommended where coverage and range is more important.
Wireless access point devices operating according to IEEE 802.11n in the 2.4 GHz spectrum may provide at least 11 defined operating channels. Wireless access point devices operating according to IEEE 802.11n or IEEE 802.11ac and generating a WLAN in the 5 GHz spectrum may provide a greater number of operating channels, the number being different in different countries.
Some of the radio channels used by WiFi systems in the 5 GHz unlicensed band are shared with radar, however. Radar is the primary user (i.e. it has priority), so it is mandated that WiFi systems such as wireless access points must monitor for radar signals, and if they detect them, must stop using those channels. This process is known in the WiFi industry as “Dynamic Frequency Selection” or DFS.
To use a “DFS” channel, a WiFi access point must first perform a “Channel Availability Check” (CAC), during which it listens without transmitting for a period of time (generally 1 or 10 minutes depending on the channel) to determine whether radar signals are present or not. If the channel is clear, the access point can then use the channel, but it must perform ongoing “In Service Monitoring” (ISM) while using the channel. Performing ongoing ISM is technically more challenging than performing a CAC.
While there are regulatory requirements that must be satisfied during testing, relating in particular to the minimum successful detection rates for (simulated) real radar signals, there is no such requirement relating to the false detection rate.
Referring to prior art documents, an ETSI Draft document ETSI EN 301 893 V1.7.2 dated July 2014 and entitled “Broadband Radio Access Networks (BRAN); 5 GHz high performance RLAN; Harmonized EN covering the essential requirements of article 3.2 of the R&TTE Directive”, available online at www.etsi.org, includes a section (Section 4.7) entitled “Dynamic Frequency Selection (DFS)” which sets out the DFS-related technical requirements and their applicability for various operational modes.
Table D.4 of the same ETSI Draft document, entitled “Parameters of radar test signals”, outlines the characteristics of the signals used to simulate radar for DFS testing purposes.
CN105307186 (“Huawei”) relates to a method for sending information, and refers to the problem that Wireless Local Area Network (WLAN) devices can take a long time to perform radar detection. The method involves an Access Point performing a Channel Availability Check for a first channel to determine whether a radar signal exists in that channel, and if so, sending a CAC result to a WLAN control device or another Access Point, the CAC result comprising the identifier of the first channel.
EP1562333 (“Sony”) relates to wireless communication systems, apparatus and methods for implementing radar wave detection. In particular, it relates to systems, apparatus and methods for establishing communication among a plurality of wireless stations that constitute, for instance, a wireless LAN, and to wireless communication systems, apparatus and methods for allowing various communication stations to perform network operations in an autonomous distributed manner without using any specially installed control station. More specifically, it relates to systems, apparatus, methods and computer programs for sharing the same frequency band with a radar wave system by making a frequency change in response to a radar wave detection in an autonomous distributed communication environment, and for detecting radar waves and making frequency changes in an autonomous distributed network while considering the power consumption of each communication station.
US2010290414 (“Yamada”) relates to a wireless communication device, system and method in which one of two access points, on detecting radar/radio signals, notifies the other access point of a change of a communication channel to a newly allocated channel, and actually changes the communication channel to the newly allocated channel.
EP3026947 (“NEC Corp”) relates to a wireless LAN access point and to a wireless communication method that aims to prevent interference with a weather radar. An access point includes detection means detecting a radar signal; detection notification means notifying a different access point that the radar signal is detected; assessment means assessing whether or not the access point has authority to determine a channel to be used between the access points; determination means determining, when the access point has the authority, the channel to be used between the access points upon detection of a radar signal by the detection means or upon detection notification of a radar signal from the different access point; channel notification means notifying the different access point of the channel determined by the determination means; and change means changing a channel used with the different access point to the channel determined by the determination means or a channel notified from the different access point.
US2016198424 (“Luo et al”) relates to a method and an apparatus for setting up an interface between access points.
IEEE Standard 802.11h, Amendment 5: “Spectrum and Transmit Power Management Extensions in the 5 GHz band in Europe” available online at www.ieeexplore.ieee.org specifies the extensions to IEEE 802.11™ for wireless LANs providing mechanisms for DFS and transmit power control (TPC) that may be used to satisfy regulatory requirements for operation in the 5 GHz band in Europe.
US2006082489 (“Liu et al”) relates to a radar presence alert for a wireless LAN.
US2017041954 (“Tsai et al”) relates to systems and methods for selecting available channels free of radar signals from a plurality of 5 GHz radio frequency channels.
WO15130336 (“Kenney et al”) relates to access points and to a method for co-existence of WiFi and airborne radars in the 5 GHZ band.
WO16159852 (“Ericsson”) relates to methods, arrangements and units for radar detection in a wireless communication system operating in a spectrum shared with a radar system.